This disclosure relates to a hydraulic system comprising a high pressure fluid source and a hydraulic actuator fluidly connected to the high pressure fluid source, and a low pressure fluid system fluidly connected to the hydraulic actuator via a fluid return line, and a hydraulic valve, wherein the hydraulic valve comprises a return spring and an elongate member, which is movably arranged in its longitudinal direction for controlling a fluid flow, and wherein the elongate member is biased to a closed position by means of the return spring. The hydraulic system is particularly suitable in a fuel injection system for supplying low-viscosity fuel, such as dimethyl ether (DME), a combustion engine. However, the hydraulic system may alternatively be implemented in various other types of applications, for example in various sorts of mobile hydraulic systems, such as for example hydraulic systems in heavy trucks, construction vehicles, busses, marine vehicles, etc.
Leakage of fluid is a general problem in hydraulic systems, such as for example leakage of fuel past a hydraulic valve in a fuel injection system, in particular when using low-viscosity fuel such as dimethyl ether (DME). It is for example known from WO2009/110820 to provide the fuel injection system with automatic isolating valves at selected locations throughout the fuel injection system, to provide a small check valve at the outlet of each injector, as well as provide a pressure regulator in the return line. These solutions however have problems in terms of long-term sealing reliability, as well as high system cost. There is thus a need for an improved hydraulic system removing the above mentioned disadvantage.
It is desirable to provide a hydraulic system where the previously mentioned problem is at least partly avoided.
The invention concerns, according to an aspect thereof, a hydraulic system comprising a high pressure fluid source and a hydraulic actuator fluidly connected to the high pressure fluid source, and a low pressure fluid system fluidly connected to the hydraulic actuator via a fluid return line, and a hydraulic valve, wherein the hydraulic valve comprises a return spring and an elongate member, which is movably arranged in its longitudinal direction for controlling a fluid flow, and wherein the elongate member is biased to a closed position by means of the return spring.
The invention is characterized in that the elongate member forms a needle, that the hydraulic valve comprises needle receiving body having a needle seat and that the needle is engageable with the needle seat so as to control the fluid flow.
Providing a hydraulic, valve with a needle and an associated needle receiving body having a needle seat enables manufacturing of a very wear-resistant valve with a very reliable long term sealing performance. In particular if the needle and needle receiving body are manufactured with tolerances and material qualities similar to those of a nozzle needle and nozzle body of a conventional diesel fuel injection nozzle, an inexpensive high performance hydraulic valve can be manufactured that may be used in many different configurations for different types of fluid flow control, such as pressure-relief valve, pressure regulating valve, pressure-isolating valve or non-return valve in a hydraulic system. Standard diesel nozzles are generally extremely precisely manufactured valves with very hard wear-resistant seats. Consequently, the solution according to the disclosure enables simplification and cost reduction of a hydraulic system and improved sealing durability and reliability.
Further advantages are achieved by implementing one or several of the features of the dependent claims.
According to an aspect of the invention, the hydraulic system is a fuel injection system for an internal combustion engine having at least one combustion cylinder, wherein the actuator is a fuel injector having a fuel injection nozzle for injecting fuel into the combustion cylinder, wherein the low pressure fuel system comprises a fuel tank, and wherein the needle is engageable with the needle seat so as to control the fuel flow. The hydraulic valve according to the disclosure is advantageous for use in hydraulic system having relatively small fluid flow volumes, such as for example fuel injection systems. In particular low-viscosity fuel injection systems can advantageously use the hydraulic valve due to the long term high performance sealing capacity providable by the hydraulic valve according to the disclosure.
According to an aspect of the invention, engaging surfaces of the needle and the needle seat are conically shaped. This increases the sealing performance, reliability and durability over time since the sealing surfaces automatically can adopt to wear of the surfaces.
According to an aspect of the invention, the needle comprises at least one thrust surface configured to be subjected to a fluid pressure for urging the needle away from the needle seat. The pressure of the fluid at the thrust surface of the needle generates a force for urging the hydraulic valve to an open state.
According to an aspect of the invention, engaging surfaces of the needle and the needle seat comprises metal for a metal to metal contact in the closed position of the hydraulic valve. Moreover, the needle seat is free from any additional soft sealing ring. Similar to above, this increases the sealing performance reliability and durability over time
According to an aspect of the invention, the needle receiving body comprises an internal bore forming a cylindrical guide for axially guiding the needle within the needle receiving body, wherein the cylindrical guide is located at a distance from the needle seat, and wherein an outlet chamber is provided between the needle seat and the cylindrical guide. The guide enables a very precise longitudinal motion of the needle within the needle receiving body, thereby reducing the wear on the needle and needle seat due to reduction of the freedom of motion of the needle. The position of the outlet chamber between the needle seat and the cylindrical guide is the result of the conventional use of the needle and needle receiving body as fuel injection nozzle, because the owlet chamber is then used a high pressure fuel receiving chamber where the fuel may urge the needle towards an open position be acting on a thrust surface of the fuel receiving chamber. The outlet chamber thus also comprises a thrust surface of the needle.
According to an aspect of the invention, the cylindrical guide forms part of a needle chamber, which is located on the side of the cylindrical guide opposite to the outlet chamber. The needle chamber may be fluidly connected to the outlet chamber or not, thereby enabling configuration of the hydraulic valve according to the specific requirements of each unique application. The fluid pressure within the outlet chamber urges the needle towards an open position and the fluid pressure within the needle valve urges the needle to a closed position, and the cylindrical guide is preferably provided with a certain level, of sealing performance for avoiding fluid leakage past the cylindrical guide. The diametric clearance between the cylindrical guide and needle is preferably less than five micrometers for accomplishing said certain level of sealing performance along the cylindrical guide. Furthermore, an additional seal can be provided along the cylindrical guide for further enhancing the sealing performance along the cylindrical guide.
According to an aspect of the invention, the diameter of the cylindrical guide is larger than the diameter of the nozzle seat.
According to an aspect of the invention, the needle receiving body comprises a single hole having a diameter greater than 1 mm upstream of the needle seat. This size enables a sufficiently large fluid flow in certain flow control applications where the standard injection holes located on the tip of the fuel injection nozzle body is too restrictive.
According to an aspect of the invention, a truncation diameter of a tip of the needle is greater than 85% of a seat diameter.
According to an aspect of the invention, a truncation angle of a tip of the needle is greater than 140 degrees. This enables a relatively large fluid flow in an open state of the needle. A more pointed tip of the needle reduces the available flow area through the needle seat.
According to an aspect of the invention, the shortest distance between the cylindrical guide and the needle seat is at least ten times the needle seat diameter. This proportion illustrates the significant length versus diameter of the needle and needle receiving body, which proportion is required when using the hydraulic valve as a conventional fuel injector.
According to an aspect of the invention, the needle and needle receiving body are parts of a fuel injection nozzle, wherein the needle is a nozzle needle and the needle receiving body is the nozzle body. Various modifications may be made to the fuel injection nozzle to make the needle and needle receiving body better suitable for the new use, such as increasing the flow area through the needle receiving body to the tip of the needle valve, increasing the flow area along the flow passage between the needle tip and outlet chamber, flatten the tip of the needle to enable an increased flow area through the needle seat in an open state of the hydraulic valve. Using parts of a conventional diesel fuel injection nozzle for constructing a hydraulic valve provides the valve with very long term high performance sealing capacity against fluid leakage, in particular low-viscosity fuel, such as dimethyl ether (DME). This is possible because a diesel fuel injection nozzle is an extremely precisely manufactured valve with very hard wear-resistant seats.
According to an aspect of the invention, the fuel injection nozzle comprises an inlet, an outlet, and the fuel injection nozzle is fluidly connected such that the pressure of the fluid supplied via the inlet of the fuel injection nozzle to the tip of the needle urges the needle away from the needle seat to open the fuel injection nozzle.
According to an aspect of the invention, the hydraulic valve comprises a valve housing for receiving the needle and needle receiving body. The valve housing enables fuel to be conveyed via suitable fluid ports of the housing to the appropriate regions of the needle and needle receiving body. The housing is preferably made of metal, such as steel, or other types of material such as plastic. The housing preferably comprises at least two main parts that are configured to enclose the needle and needle receiving body. The housing may even be integrated with a housing of the actuator to form a common housing containing both the actuator and the hydraulic valve.
According to an aspect of the invention, the valve housing preferably comprises a fuel inlet configured to supply relatively high pressure fluid to the contact region of the needle and needle seat for urging the needle away from the needle seat.
According to an aspect of the invention, the hydraulic valve comprises a fluid outlet fluidly connected to the outlet chamber and/or a fluid outlet fluidly connected to the needle chamber.
According to an aspect of the invention, the inlet of the hydraulic valve is connected to the high pressure fluid source and the outlet of the hydraulic valve is connected upstream of the actuator for preventing backflow of fluid towards the high pressure fluid source. The hydraulic valve prevents backflow during time periods where the high pressure fluid source is disabled or for other reasons does not supply high pressure fluid.
According to an aspect of the invention, the inlet of the hydraulic valve is connected upstream of the actuator and the outlet of the hydraulic valve to the return line or the low pressure fluid system for limiting the pressure of the fluid supplied to the actuator. The hydraulic valve function here as a pressure relief valve that protects the actuator from harmful over pressures.
According to an aspect of the invention, the inlet of the hydraulic valve is connected to the outlet of the actuator and the outlet of the hydraulic valve is connected to the return line or the low pressure fluid system for regulating the operating pressure upstream of the hydraulic valve and/or preventing backflow of fluid towards the actuator.
According to an aspect of the invention, the needle chamber is connected to atmosphere. The air within the needle chamber may thus easily be pushed out of the needle chamber in case of opening of the hydraulic valve, such that the fluid in the needle chamber does not act as resistance against the opening motion of the needle. This arrangement requires good sealing performance along the cylindrical guide to avoid fluid leakage out from the hydraulic valve along the cylindrical guide.
According to an aspect of the invention, the needle chamber is connected to the low pressure fluid system. The current pressure of the low pressure fluid system will thus act on a thrust surface of the needle in the needle chamber for urging the needle to a closed position in conjunction with the return spring. Thus configuration of the hydraulic valve thus results in different opening characteristic than where the needle chamber is coupled to atmosphere.